Phase formation and reaction kinetics in M–Sn systems (M = Zr, Hf, Nb, Ta, Mo)

Abstract

A systematic search for metal ‐ tin systems which show a potentially high remelting temperature in diffusion-soldered bonds was done by investigation of phase formation and reaction kinetics in M ‐ Sn systems (M = Zr, Hf, Nb, Ta, Mo). Phase equilibration experiments were done with powder samples prepared from pure elements, heated in evacuated silica capsules between 300 and 1000 ∞C for 1 h to 200 days, and studied by X-ray diffraction analysis. Diffusion couples M/Sn (M = Zr, Nb, Ta, Mo) were prepared from the foils of pure elements and heated in a bonding furnace or in evacuated silica tubes at 300 ‐ 700 ∞C for 6 ‐ 95 h. The couples were cross-sectioned and studied by scanning electron microscopy with energy-dispersive X-ray analysis. The rates of M ‐ Sn reactions can be semiquantitatively ordered in the sequence Zr > Nb > Hf > Ta 4 Mo (‐ Sn). The activation energy of the better defined reactions Zr ‐ Sn, Nb ‐ Sn, Hf ‐ Sn are in the range of 67 ‐ 93 (‘ 15) kJ/mol. A Ta ‐ Sn phase diagram was constructed with similarities to the V ‐ Sn system. Only Zr ‐ Sn is a potential candidate for diffusion soldering of high-temperature stable bonds, Mo is suggested as an effective diffusion barrier against the attack of liquid tin.